the usual down town setting
Well, Transformer's armor is far stronger than Chitauri's vehicle. Chitauri army can be taken down by conventional weapon, even a pistol (evident by Black Widow) will kill them, Decepticons endured missiles fired from F-22 and many heavy arsenal.
Stronger Transformers were found in Dark of the Moon, I'm not sure if they can handle that. Chitauri's weapon simply inflict non-fatal injury to Captain America while Decepticon's weapon easily vaporize humans, I'll take that back, I'm not sure if movie Hulk could endure it, but he is very agile.